The major emphasis of this research will be a study of phospholipase A2 action on lipid membrane systems. In addition, interactions of melittin and a sterol carrier protein with lipid membrane systems will be studied. Current studies will be carried on the effects of surface charge and non-substrate amphiphiles on phospholipases A2 from porcine pancreas and Crotalus adamanteus. The effects of molecules such as dialkylphosphates, salicylates, diglycerides and zwitterionic detergents in monolayer, micellar and liposomal systems will be studied in order to understand the mechanisms of inhibition and activation below and above the normal cutoff pressures of these enzymes with pure substrate. Differential substrate specificity in mixed lipid systems will be studied in monolayer systems as a function of surface pressure and also in micellar and liposomal systems. Fluorescence spectroscopy will be used in addition to kinetic techniques to determine binding at the enzyme active site and interactions of the enzyme at lipid interfaces (penetration). A membrane phospholipase A2 from erythrocytes will be isolated by affinity chromatography. Properties of this enzyme including substrate specificity, surface pressure and charge effects, and possible hormonal effects will be studied and compared with those of the soluble enzymes. The interaction of melittin with liposomal membrane systems will be studied with respect to its effect o structural organization of membrane lipids and enhancement of phospholipase activity. Finally, lipid interactions with asterol carrier protein isolated from rat blood and necessary for microsomal metabolism of steroids will be investigated in collaboration with Dr. Mary DempsAy (University of Minnesota). Of particular interest is its interaction with and specificity for cholesterol and related steroIds. This will involve the use of monolayer techniques and fluorescence spectroscopy.